Dog is a type of animal that lives with humans as pets, guard dogs, herding dogs, hunting dogs or assistance dogs. Thirty million dogs live in the United States, where they are commonly called man’s best friend. They are playful, loving, loyal and listen to their owners. Dogs are also used as therapy pets, reducing stress, anxiety and loneliness, encouraging exercise, playfulness and even lowering blood pressure.
The modern dog evolved from wolves during the Late Pleistocene, about 100,000 years ago. During the domestication process, dog breeds were developed for herding and guarding livestock, tracking wounded game or finding objects lost in snow and water. Herding dogs, pointers and retrievers are a few examples of breeds developed to assist hunters. Smaller breeds such as Pekingese and Chihuahuas were bred for lap dogs and companions.
Today, many dogs are trained to serve as guide dogs for the blind and help the police in their work by detecting bombs or illegal drugs. They also work with customs officials patrolling for rat-infested cargo at distant harbors or sniffing out forest insect pests in shipments of wood from overseas. Some dogs are even trained to smell for diseases in the human body.
Though some dogs are naturally obedient and willing to please, most require training. The temperament of a dog is determined by its genetics, early socialization and environment. A person who wants to understand a dog must look at the whole picture, including body language, behavior and context. For instance, panting does not necessarily mean that the dog is anxious; it may simply be hot. Similarly, yawning does not always indicate that the dog is tired; it could be a sign that the dog has picked up a scent.